The invention relates generally to components of the hot section of gas turbine engines, and more particularly, to a process for depositing a coating onto a selective area of a turbine component.
In gas turbine engines, for example, aircraft engines, air is drawn into the front of the engine, compressed by a shaft-mounted rotary compressor, and mixed with fuel. The mixture is burned, and the hot exhaust gases are passed through a turbine coupled to a shaft. The flow of gas turns the turbine, which drives the compressor. The hot exhaust gases flow from the back of the engine, providing thrust that propels the aircraft forward.
During operation of gas turbine engines, at least some components within the engine, maybe in contact with high temperature gases. Such components may include, for example, blades, vanes, and nozzles used to direct the flow of the hot gases.
To facilitate shielding the metallic parts from the combustion gases, environmental coatings may be applied to the components. Such environmental coatings may be produced by holding the part to be coated at a temperature in an atmosphere that is rich in a certain element or elements, often aluminum. The elements diffuse onto the surface of the part and form a diffusion coating in a process known as diffusion aluminide. In one form, the environmental coating is fabricated from a diffusion cobalt aluminide, nickel aluminide or platinum aluminide. The diffusion aluminide coating surface forms an aluminum oxide scale when exposed to oxygen-containing atmospheres at elevated temperatures, thus facilitating increased resistance to additional high temperature oxidation.
At least some other known component coating processes demand labor-intensive processes. For example, when the component is a low pressure turbine (LPT) nozzle, known coating processes require a labor intensive masking process wherein a commercially available aluminum gettering masking tape is applied to the desired area of the turbine component. More specifically, the tape is affixed in place using a sheet metal strip. However, continued exposure to the high temperatures utilized by the coating process, may cause the sheet metal strip to warp, such that the strip fails to provide adequate support for the masking tape. As a result the masking tape may undesirably dislodge from the component during the aluminide coating process, and an undesired area of the turbine nozzle may be aluminided.